Method and device for production of endless plastic hollow profiles

ABSTRACT

A method for production of endless plastic hollow profiles, in particular tubes, comprises several production stages for the plastic tube and a coating stage for a metal coating. A reduced pressure is provided in the coating stage, whereby the metal is transferred into the gas phase and deposited on the tube as a surface layer homogeneously bonded thereto.

[0001] The invention relates to a method of producing endless plastichollow profiles, particularly tubes, as well as to a device for carryingout the method, consisting of several production stages for the plastictube and a stage for application of an outer metal casing.

[0002] Coatings of plastic materials by means of thin-layer technologyare known particularly in the packaging industry. In that case a minimummetallic layer is applied at one side at high speed to a plastic film.This known method is not usable for the circumferential surface ofhollow profiles, particularly tubes, to which a layer with uniformthickness is to be applied, since in accordance with this method filmscan always only be coated at one side.

[0003] The invention is therefore based on the object of creating, forhollow profiles, a method by which a technically usable metal coatingcan be produced in accordance with thin-layer technology at highproduction speed.

[0004] According to the invention this object is fulfilled in that themethod according to the category is designed also according to thecharacterising part of claim 1.

[0005] Refinements and developments of the invention are claimed in thesubclaims.

[0006] A device for carrying out the method is described as an examplein the drawings, in which:

[0007]FIG. 1 shows a schematic view of a coating plant, wherein the tubeissues from an extrusion plant,

[0008]FIG. 2 shows a schematic view of a coating plant, wherein the tubeis unwound from a reel, and

[0009]FIG. 3 shows the schematic format of the coating stage.

[0010] A known device 1 for producing a plastic tube t, for example ofpolyethylene, consists of an extruder 11, a tool 12, a calibrating path13, a cooling path 14, a possibly desired printer 15, a withdrawal path16 for drawing the plastic pipe t in the direction of the arrow a, acutter 17 and a reel 18 for winding up very long pipe lengths.

[0011] According to the invention a system of three stations for coatingthe plastic tube t with a metal is inserted preferably between thecooling path 14 and the printer 15.

[0012] The tube surface after exit of the tube t from the tool 12 isuneven with a cratered form and in this state is not suitable for directcoating. The tube t therefore initially runs through a smoothing path 22in which a liquid polymer is applied to the tube surface. In thefollowing drying path 21 the applied polymer layer is dried. The tubesurface is thereafter suitable for coating.

[0013] Instead of application of a liquid polymer, the tube surface canalso be smoothed by exposure to flame.

[0014] Subsequently, the thus-pretreated tube t runs through the coatingpath 2. The internal format of the coating path 2 is illustratedschematically in FIG. 3. Disposed in the interior of the coating path 2are, for example, four flame treatment modules 231, 232, 233, 234, whichare displaced relative to one another in each instance by an angle of 90degrees so that a uniform coating of the tube t takes place. However, itis also possible to mount the modules to be movable and to let themcirculate around the tube t during the coating. The flame treatmentmodules are electrically heated and evaporate the coating metal, forexample aluminium or copper, so that this is transferred into the gasphase and deposits on the tube t. An underpressure preferably prevailsin the coating path 2. Due to the very smooth surface of the tube t,expensive sealing measures are not necessary.

[0015] A liquid lock, as is known for vacuum containers in continuousproduction processes, would also be highly disadvantageous for coatingin vacuum, since the surface of the tube if wetted by the liquid is nolonger capable of being coated. The seals 241, 242 are therefore plasticseals of resilient material.

[0016] In the afore-described device 1 it is necessary to design thedifferent lengths of the smoothing path 22, drying path 21 and coatingpath 22 transited by the tube t so that these can fulfil their tasks atthe preset production or extrusion speed.

[0017] In FIG. 2 there is reproduced a device 1 in which the tube t tobe coated is already present and wound up on a reel 18. It then runsthrough only the paths 22, 21, 2. In this case the transit speed throughthe paths 22, 21, 2 is no longer dependent on a production speed, butcan be designed exclusively in accordance with the requirements of thethree paths 22, 21, 2.

[0018] It is feasible to combine the three paths 22, 21, 2 into a unit.In this case only two seals are required.

Reference Numeral List

[0019]1 device

[0020]11 extruder

[0021]12 tool

[0022]13 calibrating path

[0023]14 cooling path

[0024]15 printer

[0025]16 withdrawal path

[0026]17 cutter

[0027]18 reel

[0028]181 reel

[0029]2 coating path

[0030]21 drying path

[0031]22 smoothing path

[0032]231 flame-exposure module

[0033]232 flame-exposure module

[0034]233 flame-exposure module

[0035]234 flame-exposure module

[0036]241 seal

[0037]242 seal

[0038] t plastic pipe

[0039] a arrow of the movement direction

1. Method of producing endless plastic hollow profiles, particularlytubes, wherein the plastic tube is initially smoothed and subsequently ametal is applied to the tube as a metal layer by evaporation in vacuum,characterised in that initially a liquid polymer and subsequently themetal layer, which intimately connects with the liquid polymer, areapplied to the smoothed tube in a mutually gas-tight layer thickness. 2.Plastic hollow profile, particularly tube, with an outer metal layeraccording to the method of claim 1, characterised by a layer of a liquidpolymer between the smoothed tube and the metal layer.